An NMR imaging system is a device that generates 2-D or 3-D sample images based on the principles of NMR imaging, and is more and more widely used in the medical diagnosis field. An NMR system normally comprises a magnet for generating a static uniform magnetic field B0 that is large enough to cover the imaged region of the patient body; a radio frequency (RF) system comprising an RF transmit coil for exciting the resonance of the sample and an RF receive coil for receiving resonance signals from the sample; a gradient system for generating a gradient magnetic field in the sample space and ensuring convenient image coding; and a computer imaging system for receiving the signals collected by the RF receive coil and generating visual images that can be conveniently observed by the doctor.
In the NMR imaging technique, the receive coil collects the RF signals from the excited sample, and the collected RF signals are then magnified for sample image reconstruction. The electrical structure of the receive coil comprises a coil body made of conducting materials; and inductors and capacitors that are connected into the coil body. When the receive coil works, it surrounds the examined region of the patient and its output impedance matches a back-end data collecting device. Moreover, uniform electromagnetic field distribution is achieved inside the coil at the operating frequency, and output resonance signal has an excellent signal to noise ratio (SNR) so as to gain a sharp and undistorted sample image. When the receive coil idles, it is detuned and does not affect the function of the transmit coil and other devices in the system.
In current techniques, a multiple channel NMR receive coil is usually constructed comprising two or more closed unit loops that surround the periphery of the imaged region. By increasing the number of the unit loops, a stronger electromagnetic signal theoretically may be obtained in less time, but more complicated tuning is necessary to gain an excellent SNR and a sharp sample image. The reason is that as the channels increase, the coupling of unit loops becomes more complicated. The coupling of adjacent unit loops can be eliminated by an overlap or by a direct series connection of inductors and capacitors. However, the coupling of nonadjacent unit loops is difficult to eliminate. If the coupling of unit loops cannot be eliminated, a multiple channel coil will not properly function.